The purpose of this project is to study the release of histamine from blood basophils and mast cells as one of the immunological mechanisms implicated in inflammation. Histamine-releasing agents studied included IgE antibody, formyl methionine peptides and a complement factor (C5a) derived from human serum. The mechanisms of these histamine-releasing activities were compared and it was concluded that C5a and fMet peptides release histamine by similar, but not identical mechanisms, and that both reactions differ from IgE-mediated release. The research is being expanded to determine the role of dental plaque in histamine-liberating reactions. BIBLIOGRAPHIC REFERENCES: Hook, W.A. and Siraganian, R.P.: Complement-induced histamine release from human basophils. III. Effect of pharmacologic agents. J. Immunol. 118:679-684, 1977. Ida, S., Hook, J.J., Siraganian, R.P., and Notkins, A.L.: Enhancement of IgE-mediated histamine release from human basophils by viruses: Role of interferon. J. Exp. Med. 145:892-906, 1977.